42nd Lunar and Planetary Science Conference (2011) 2547.pdf

CORRELATION OF LOW-ALBEDO DEPOSITS ON THE FLOORS OF OUDEMANS CRATER AND SOUTHEAST . S.C. Mest1,2, C.M. Weitz1, and L.L. Tornabene3, 1Planetary Science Institute, 1700 E. Ft. , Suite 106, Tucson, AZ 85719-2395 ([email protected]); 2Planetary Geodynamics Labora- tory, Code 698, NASA GSFC, Greenbelt, MD 20771; 3Center for Earth and Planetary Studies, Smithsonian Institu- tion, PO Box 37012, National Air and Space Museum, MRC 315, Washington, D.C. 20013-7012.

Introduction: HiRISE and CTX images provide currence of these deposits in the central peak indicates detailed views of the allowing geologic they may have originated at a depth of ~7-11 km; this materials to be characterized with regard to meter-scale excavation depth is based on a transient crater diameter morphologies and textures. Such images reveal un- of 70 to 110 km [11,12] and a theoretical sampling precedented detail of unique deposits within the canyon depth of approximately one-tenth the apparent crater of eastern Noctis Labyrinthus (NL) that may be related diameter [13,14]. Although similar in appearance, these to the Oudemans impact [e.g., 1-7]. Dark rugged mate- depths are at the maximum or greater for LTLDs ex- rials, mantled by eolian sediments, are observed to ex- posed on the floors of NL and VM. However, the expo- tend from the floor of Oudemans into NL. Further sure of these materials in the outer portion of the central northwest of Oudemans, the floor of NL contains depos- structural uplift suggests that may originate from shal- its that display complex morphologies consisting of lower depths than estimated here. flow-like structures, and in some cases complexly The floor of Oudemans is covered primarily by a folded and rugged massifs, some of which contain light- mottled (in THEMIS day IR) deposit that extends across toned materials. These deposits are unique to this part of the entire crater floor, through the breach in the northern NL or to the east. Here we use HiRISE rim, and into NL as far as ~50-75 km northwest of the and CTX images to investigate the probable origins of crater. These materials appear to embay the - these deposits as they relate directly or indirectly to aged plateau materials. These areas consist of materials Oudemans, including (1) Oudemans ejecta, impact melt previously mapped as -aged smooth floor and/or impact breccia, or (2) landslide deposits gener- material (believed to be alluvial and eolian in nature) ated by Oudemans impact-induced quakes. and slide material (derived from NL wall materials) [8]. Observations: Here we morphologically character- In THEMIS day IR images, the slide material shows ize the deposits within Oudemans and NL to the north flow-like morphology suggesting possible emplacement (Fig. 1), and map their spatial distributions in order to via mass movements. However, HiRISE and CTX im- evaluate their relationship to the crater. ages of these deposits, as well as upslope, display no Oudemans Crater: Oudemans (D~120 km; 9.8°S, landforms that resemble landslides or other mass 268.2°E) appears to be a well-preserved crater, esti- movement mechanisms. Furthermore, examination of mated at Late to Early Amazonian in age [8], the plateau and canyon floor reveal no channels or fea- and displays well-preserved continuous ejecta, crater tures that could have provided a conduit for alluvium to rim, terraced walls, and central peak. There is a large be transported and deposited in this part of NL. The gap in the northern section of the crater wall where it overall morphology of these deposits is also inconsistent intersects the canyon. This is likely the result of the in- with eolian deposition. Here, high-resolution images tersection of the “displaced zone” with deep portions of reveal mottling is due to dark- and light-toned areas that the valley system to the north (i.e., Oudemans post- exhibit distinct surface morphologies (Figs. 2 and 3). dates the formation of the valley system), or the wall Dark areas consist of rugged massifs that contain a was subsequently removed as the canyon formed or the combination of small knobs (especially in its southern canyon enlarged. Oudemans ejecta is not “layered” – extent) and shallow pits and degraded small-diameter atypical of Martian craters of this size [9] – instead, the impact craters. Light-toned areas, especially in the east- ejecta appears to be hummocky and more “ballistic” in ern and northwestern parts of this deposit, coincide with nature. The ejecta is also asymmetric in planform, being dune-forming sediments that fill low-lying areas among broader to the east and west, narrower to the , and the darker massifs. Intermediate-toned areas consist of indistinct from NL floor deposits to the north. The lack dark rugged materials covered by a thin mantle of of a wall and apparent lack of ejecta to the north of brighter materials, possibly consisting of dune-forming Oudemans, and the asymmetric ejecta pattern suggest an sediments. The morphology of this dark material in oblique impact may be possible and account for some of high-resolution images suggests this deposit could be Oudemans’ appearance. Oudemans impact-melt-bearing material emplaced in The central peak of Oudemans displays Light- NL, and is currently being buried by eolian sediments. Toned Layered Deposits (LTLDs) that exhibit alternat- Noctis Labyrinthus: The floor of NL northwest of ing light- and dark-toned strata cut by fractures and are Oudemans was previously mapped as Amazonian-aged tilted near vertical [3,7], which is also common in other rough floor material, interpreted to be debris eroded smaller complex craters to the southeast [10]. The oc- from NL canyon walls and/or landslide material man- 42nd Lunar and Planetary Science Conference (2011) 2547.pdf

tled by eolian deposits [8]. However, in addition to be- timing of the emplacement of these deposits relative ing chaotic in appearance (Fig. 4), this deposit exhibits tothe formation of Oudemans (such as by crater size- scattered knobs, clusters of light-toned blocks within a frequency distribution statistics). darker matrix, scarp-bounded smooth moderate- and low-albedo mesas, and pits with elongated and irregular References: [1] Edgett, K.S., and M.C. Malin (2004) 35th shapes. Massifs within this deposit, which are likely LPSC, Abs. #1188. [2] Tornabene et al. (2006) 37th LPSC, Abs. #1739. [3] Beyer et al. (2007) 7th International Conf. on remnants of the Noachian basement, appear to be man- th tled by the low-albedo mesa-forming material and in , Abs. #3310. [4] Weitz et al. (2007) 38 LPSC, Abs. #1442. [5] Weitz et al. (2008) GRL, 35, L19202. [6] Weitz et some cases this mantle is being removed from the mas- al. (2010) 41st LPSC, Abs. #2240. [7] Quantin et al. (2009) sifs, but remains along the lower massif slopes. Materi- 40th LPSC, Abs. #1651. [8] Witbeck et al. (1991) Geologic als exhibiting this surface morphology are only found in Map of the Valles Marineris Region, Mars, I-2010, 1:2M this location in NL, proximal to Oudemans, and sug- scale. [9] Barlow, N.G. (2004) GRL, 31, L05703. [10] Caudill, gests that they could be related to the Oudemans im- C. (2011) submitted to 42nd LPSC, this volume. [11] Croft, pact-forming event. S.K. (1985) JGR, 87, C828-C842. [12] Grieve, R.A.F. and Discussion: This is an ongoing investigation into A.M. Therriault (2004) M&PS, 39, 199-216. [13] Ivanov et al. the nature of deposits within Oudemans crater and a (1982) Meteoritika, 40, 67-81. [14] Melosh, H.J. (1989) Im- unique series of deposits to the north within NL. Previ- pact Cratering: A Geologic Process, 245pp. ous Viking-based studies suggested these deposits are comprised of Amazonian-aged alluvial and/or eolian sediments, or materials emplaced via landslides from plateau wall materials. However, analysis of recent high-resolution HiRISE and CTX images suggests that these deposits may be directly related to the Oudemans impact, consisting of impact-melt-bearing material re- leased from the crater via the breached northern wall and turbulently emplaced ejecta confined within the canyon of NL. Future work will involve continued Figure 2. Rugged dark material on floor of Oudemans and mapping and evaluation of this relationship, and the Noctis Labyrinthus to north. CTX P05_003079_1714.

Figure 3. Rugged massifs Figure 4. Chaotic terrain on Figure 1. MOLA DEM over THEMIS day IR mosaic (100 surrounded by smooth mate- floor of NL, northwest of m/pixel) showing locations of Oudemans, Noctis Labyrinthus rials on floor of Noctis Oudemans. HiRISE image (NL) and Valles Marineris (VM). Red circle represents ap- Labyrinthus just north of ESP_018190_1720. proximate extent of continuous ejecta from Oudemans (~1½ Oudemans. HiRISE image times Oudemans diameter). Blue lines represent THEMIS- PSP_005624_1715. derived contacts. Dots represent HiRISE images displaying LTLDs found within the expected Oudemans ejecta (red) and beyond the ejecta (blue). Yellow oval shows location of possi- ble Oudemans-related features found within NL.